Electrolytic apparatus for preparation of organometallic compounds

ABSTRACT

Electrolytic apparatus for preparing organometallic compounds is disclosed. The apparatus includes anode and cathode members in the form of shot material, separated by a tubular perforate member comprising an open mesh haircurler member sandwiched between fine mesh screen, with the electrodes connected to a source of low frequency alternating current potential.

United States Patent [191 Shepard, Jr. et a1.

I ELECTROLYTIC APPARATUS FOR PREPARATION OF ORGANOMETALLIC COMPOUNDS[75] Inventors: John C. Shepard, Jr., Lake Jackson; Edward E. Johnson,Sweeny; Robert W. Bearman, Lake Jackson, all of Tex.

[73] Assignee: Nalco Chemical Company, Chicago,

Ill.

[22] Filed: Feb. 16, 1973 [21] Appl. No.: 333,041

Related U.S. Application Data [62] Division of Ser. No. 185,005, Septv30, 1971,

abandoned.

[52] U.S. Cl 20 1/260, 204/59 QM, 204/59 L, 204/283 [51] Int. Cl B01k3/10 [58] Field of Search 204/59 L, 59 OM, 260, 272, 204/275, 283, 284

[ 1 Dec. 10, 1974 [50] References Cited UNITED STATES PATENTS 3,287,2481 1/1966 Braithwaite 204/260 3,630,858 12/1971 Ganci et a1 204/59 LFOREIGN PATENTS OR APPLICATIONS 1,194,181 6/1970 Great Britain 204/260Primary Examiner-John H. Mack Assistant Examiner--W. I. SolomonAttorney, Agent, or Firm--Lockwood, Dewey, Zickert & Alex 5 7] ABSTRACTElectrolytic apparatus for preparing organometallic compounds isdisclosed, The apparatus includes anode and cathode members in the formof shot material, separated by a tubular perforate member comprising anopen mesh haircurler member sandwiched between fine mesh screen, withthe electrodes connected to a source of low frequency alternatingcurrent potential.

3 Claims, 3 Drawing Figures PATENTE'U SE8 1 (H974 FEED DRUM

sum 2 or 2 FIG-L3 I HEAT (CHANGER SURGE DRUM INITIAL CELL T EXCHANGERSURGE DRUM FINAL CELL APPARATUS FOR ELECTROLYTIC PREPARATION OFORGANOMETALLIC COMPOUNDS This is a division of application Ser. No.185,005, filed Sept. 30, 1971, and now abandoned.

It is now well known that organometallic compounds may be produced bythe electrolysis of Grignard reagents using sacrificial metal anodes.This process is particularly suitable for the production of organoleadcompounds particularly tetramethyllead and tetraethyllead. The detailsof this well known electrolytic process is set forth in the teachings ofU.S. Pat. No. 3,007,858. The invention as described in this patent issummarized by the patentee as follows:

In accordance with the invention it has been found that organo metalliccompounds can be produced by electrolyzing a substantially anhydroussolution of a Grignard reagent in an organic solvent for the Grignardreagent using a sacrificial anode and adding an organic halide to theelectrolyte, the organic radical of which corresponds to the organicradical of the Grignard reagent being used. As the electrolyzing actionproceeds. magnesium normally tends to deposit at the cathode and thisnormally causes serious problems, such as bridging between the anode andthe cathode, but the added organic halide reacts with this magnesium andreconverts it to a Grignard reagent thereby avoiding the deposit ofmagnesium at the cathode. The term organic halide as used herein isintended to include organic chlorides. bromides and iodides. The halogenportion of the added organic halide does not have to be the same as thehalogen portion of the Grignard reagent. The free hydrocarbon radicalsderived from the Grignard reagent during electrolysis combine with theanode material to form the corresponding organo metallic compound whichcan be separated from the electrolyte in any suitable manner.

cathode may be composed of the same material as the anode. Thus, inproducing tetraethyl lead both the cathode and the anode can be composedof lead. It is preferable, however, that the anode be composed of leadand the cathode of stainless steel.

The invention is particularly valuable in the preparation of tetraethyllead and this preparation will be used to illustrate the practice of theinvention. In carrying out this process a lead anode and preferably astainless steel cathode are placed in a solution of ethyl magnesiumchloride dissolved in a suitable organic solvent. A suitable organicsolvent preferably employed for this purpose is the dibutyl-ether ofdiethylene glycol. An electrolyzing current is passed into the ethylmagnesium chloride solution (Grignard solution) in sufficient amount tocause the lead anode to be dissolved. Ethyl chloride is passed into theethyl magnesium chloride solution either intermittently or continuouslyin sufficient amount to react with the magnesium liberated at thecathode to reconvert it to ethyl magnesium chloride. The free ethylradicals react at the anode with the lead to form tetraethyl lead.Magnesium chloride is a byproduct of this process. The tetraethyl leadis removed in any suitable manner from the organic solvent solution.Where a high boiling solvent is used such as dibutyl ether of diethyleneglycol, the tetraethyl lead, is treated to remove the magnesiumchloride. This can be done by adding a substance which forms aninsoluble compound with the magnesium chloride, for example, dioxane,and filtering the insoluble precipitate. The solvent solution from whichthe magnesium chloride has been removed is then recirculated to the cellin which the electrolyzing action is carried out or to a suitablecontainer where it is used as a solvent for additional quantities ofGrignard reagent. The removal of a partially electrolyzed solution fromthe electrolyzing cell is preferably agitated with suitable mechanicalstirring or other agitating means.

Over the ensuing years numerous improvements have been made in theprocess whereby it is possible to produce organo lead compoundsefficiently and on a large scale commercial basis. Typical of suchimprovements are the various techniques and procedures described in thefollowing U.S. Pat. Nos: 3,234,1 12; 3,312,605; 3,372,098; 3,391,066;3,391,067; 3,393,137; 3,409,518; and 3,497,428. The disclosures of allof these patents are incorporated herein by reference.

In preparing organo metallic compounds by the direct currentelectrolysis of Grignard reagent using sacrificial anodes severaloperating parameters must be observed if the process is to operateefficiently. It is always necessary that some Grignard reagent bepresent during all of the electrolysis procedure since experience hasshown that when the Grignard reagent is depleted electrical shortingoccurs which on large scale equipment can produce costly shutdowns. Therequirement that Grignard reagent be present at the end of electrolysisrun means that the reaction may never go to completion. Another problemthat is encountered in the large scale direct current electrolysis ofGrignard reagents to produce organo metallic compounds resides in theexpense involved in the rectification of alternating current to directcurrent. Since most electrical current produced in the world isalternating current, it must be converted by means of suitablerectifying devices, such as silicone diodes, to convert it to usabledirectcurrent. If alternating current is not rectified, then speciallydesigned direct current generators must be manufactured to provide thequantity of direct current needed to operate large scale plants.

If it were possible to electrolyze Grignard reagents to produce organometallic compounds whereby excess Grignard reagent need not be presentto prevent electrical shorts from occurring and alternating currentcould be substituted for direct current, a valuable contribution to theelectrochemical arts would be afforded.

THE INVENTION In accordance with the invention it has been found thatorganometallic compounds of the type having a carbon atom of a non-polarorganic radical linked to a metal may be prepared by electrolyzing withlow frequency alternating current a substantially anhydrous solution ofa Grignard reagent which is in contact with a sacrificial metalelectrode. Upon completion of the electrolysis the organometalliccompound is recovered by known processing techniques. The organometalliccompounds that may be produced using the process of this inventioninclude a large number of well known organometallic chemicals. Thus,organo compounds of the metals lead, zinc, tin, copper, mercury, and thelike may be synthesized. The non-polar organic radicals attached to themetals may be selected from any organic radical that is capable ofexisting in the form of a Grignard reagent. Exemplary are such organicradicals as methyl, ethyl, butyl, isobutyl, phenyl and substitutedphenacyl radicals, such as benzyl. These hydrocarbon radicals maycontain substituents thereon such as halo radicals, e.g.,trifluoroethyl. It is preferred that the organic radicals be analiphatic hydrocarbon radical and preferably any organic radical usedshould not contain more than six carbon atoms.

The process employs a Grignard reagent dissolved in a substantiallyanhydrous solvent which is chemically inert to the conditions of thereaction and which is capable of allowing a Grignard reagent to beformed therein. This solvent is further characterized as beingelectrically conductive when the Grignard reagent is present therein.Solvents of this type include, most preferably, the well-known organicethers which have been used for the preparation of Grignard reagents formany years. To maximize the electrical conductivity of the anhydrousGrignard reagent solutions, certain blends of ethers are extremelydesirable. For instance, certain blends of aliphatic ethers either aloneor in combination with cyclic ethers such as tetrahydrofuran aredesirably employed in the practice of the invention. An excellent blendof ethers in which the starting Grignard reagent may be prepared are thealiphatic glycol diethers blended with tetrahydrofuran with the latterbeing present in the range of 65 75 percent by weight which aredescribed in US. Pat. No. 3,312,605, the disclosure of which isincorporated herein by reference.

CONDITIONS OF THE ELECT ROLYSIS The alternating current electrolysis ofthe Grignard reagent may be conducted under a wide variety ofconditions. The alternating current should be of low frequency and maybe either one, two, or three phase. One phase alternating current ispreferred. By the term low frequency alternating current is meant thatthe frequency of such current in terms of cycles per second should notexceed 60 cycles. Excellent results are obtained when the frequency ofthe alternating current is within the range of to 60 cycles and mostpreferably within the range of 5 30 cycles. While the voltage may varybetween 1 60, good results are obtained when the voltage is within therange of volts. The amperage will of course vary depending upon the sizeof the particular cell used.

The electrolysis is conveniently conducted at temperatures within therange of 50- 60 C. when organolead compounds are produced. Thetemperature may be increased or decreased with the controlling factorbeing the boiling points of the organic liquids used in the electrolysisprocess.

THE ELECTRODES The electrodes may be of any of the metals previouslydescribed, e.g., those capable of being converted by Grignardelectrolysis into organometallic compounds. The electrodes may be in anysize, shape, or configuration just as long as when they are immersed inthe Grignard solution, they are electrically insulated from each other.While a preferred form of the invention dictates that the electrodes beof the metal corresponding to the organometallic compound sought to beproduced it will be understood that only one electrode need be of suchmetal. In this case the other electrode should not be sacrificial innature and hence would be composed of an inert conducting substance suchas platinum or carbon.

To illustrate a typical cell design for producing organometallic leadcompounds such as tetraethyllead or tetramethyllead reference may be hadto the drawings.

DRAWINGS FIG. 1 is a vertical cross-sectional view of a typical cellthat may be used to electrolytically produce organic lead compounds fromGrignard reagents.

FIG. 2 is a top view taken across the lines 22 of FIG. 1.

FIG. 3 is a schematic view of two series connected cells of the typeshown in FIG. I and FIG. 2 that may be employed for the continuousproduction of organolead and other organometallic compounds by thepractice of this invention.

With particular reference to the drawings, there is shown in FIGS. 1 and2 a substantially cylindrical vessel having side walls 12, a bottom 14,and top 16. Positioned in the bottom 14 is an inlet 18 which is adaptedto allow Grignard solution to enter the cell along with otheringredients that will be more fully described.

Fitted inside of the cell near the bottom is a screened support 20 uponwhich rests a Teflon plug 22. Fitted about the Teflon plug and insealing relationship there with are a series of overlayed cylindricalinsulating materials. The first such layer 24 is a fine mesh nylonscreen which is impressed upon the inner surface of a polypropylenehaircurler 25 which is a large open mesh semi-rigid lattice work ofpolypropylene which supports the nylon screen 24. Wrapped around theoutside of the haircurler 25 is another nylon screen 26 which issubstantially the same thickness as the inner nylon screen M. Goodresults are achieved when the nylon screens are from 60 mesh. Positionedwithin the opening 28 defined by the nylon screens is an electricalcontact strip 30.

Within the space 28 as well as the area outside of the space andenclosed by the cell wall 12 there are placed into the cell leadelectrodes 31 which are in the form of beebees or shot. The outside wall12 is fitted with an electrical contact strip or buss bar 32.

The top of the cell 16 is fitted with a liquid opening 34 and ispreferably sealed to the remainder of the cell by means of a Teflongasketed flange 36.

In operation the electrical contacts 30 and 32 are connected to a sourceof alternating current (not shown) and the Grignard reagent dissolved inan appropriate solvent is added to the cell through inlet 18. As thecell fills the fluid leaves the cell through outlet 34 where it isrecirculated back into the cell by means of an appropriate recycle lineand pump (not shown).

When it is desired to produce organometallic compounds, particularlytetramethyllead, continuously an arrangement of the type illustrated byFIG. 3 may be used. With particular reference to FIG. 3, there is showna feed drum which contains a Grignard reagent such as methyl magnesiumchloride dissolved in an ether solvent which preferably is a blend of 60parts by weight of tetrahydrofuran and 40 parts by weight of the diethylether of tetraethylene glycol. A preferred amount of Grignard reagent inthis solvent system is 1.5 moles per liter.

The Grignard reagent solution is removed from feed drum 110 through line112 and circulated by pump 114 through lines 115 and 116 back to thefeed drum 110. When it is desired to begin, the reaction valve 118 whichis Td to line 115 is opened and the Grignard solution flows through line120 into surge drum 122. Upon filling of surge drum 122 the Grignardsolution is removed therefrom to line 124 by means of circulating pump126 where it moves to line 128 through line 130 into electrolysis cell132. The cell is constructed in accordance with FIGS. 1 and 2 previouslydiscussed.

6 EXAMPLE 1 The cell used in this series of experiments was a /2 litercell in corresponding construction to the cell shown in FIG. 1.Alternating current was supplied by a potentiostat supplied with l 10volts 60 cycle current. Appropriate 1.5 molar solutions of methyl,ethyl, butyl, and phenyl Grignards were prepared in atetrahydrofuran-diethyl ether of tetraethylene glycol in proportionspreviously specified. Throughout the run the appropriate methyl, ethyl,butyl, or phenyl halides were added to the cell to provide about 1.0percent by weight of the total cell content. The runs were monitored byanalyzing the alkyl halide concentration and the concentration of theactive Grignard. The results of these tests Effluent from the cell isdischarged therefrom through are presented below in TABLE I.

TABLE I Run Frequency Average Average Avera e Initial Final Current No.cycles/sec. Volts Amps. Temp (OH )mm/gm (OH )mm/gm Efficiency TML l 6024 I0 80 L06 0.23 137 2 60 25 I0 78 l 39 0.ll I54 3 60 25 I0 76 0. 17 l13 TEL 4 60 26 6 75 1.00 0.77 58 5 60 3O 9 75 1.38 0.92 6l 6 60 I0 770.92 0.50 62 7 60 9 70 L 0.20 56 TBL 8 e0 37 9 77 1.44 t8 0.29 32 25 I077 L32 0.45 28 line 134 into heat exchanger 136 where it is cooled anddischarged through line 140 and returned to the surge drum 122.

As can be seen from the drawing line 128 is fitted with a control valve142 which allows feed from surge drum 122 to be transported into surgedrum 144. Surge drum 144 is fitted with a discharge line 146, acirculating pump 148 and a discharge line 150 therefrom which feeds intoa second cell 152. The effluent therefrom which passes through line 154into heat exchanger 156 and vents to line 158 into surge drum 144. Line154 is Td into product discharge line 160 which is fitted with a valve162 which allows discharge of the final cell electrolysis product.

When arrangement shown in FIG. 3 is used there is provided in the systema source of extraneous alkyl halide which is contained in storage tank164 which is discharged through line 166 into surge drum 122. The use ofthe alkyl halides is an important additive since it prevents thebuild-up of magnesium etherates, salts and the like in cell 132 whichwould require the intermittent cleaning thereof were it not for theexcess alkyl halides.

While the use of extraneous halides are required in conventional directcurrent Grignard electrolysis processes, it is not required when thepresent invention is used as a batch process. It may be employed in boththe continuous or batch process to insure efficient operation of thecell. As will be shown by the examples hereinafter presented,organometallic compounds can be produced with all of the Grignardreagents being utilized without cell shorts or substantial currentefficiency impairment occurring.

To illustrate the invention the following are presented by way ofexamples:

In the above Table the initial and final (OI-I)mm/ gm indicates theinitial and final molarity of the Grignard reagent in the cell. Thecurrent efficiency is the ratio of current used to produce lead inrelation to the total current put through the cell. Two hundred isideal. In the above experiments the average temperature was maintainedbetween 50 60 C. and the average batch time was 10 hours. It will benoted from the above Table that the current efficiencies were less whentetraethyllead and tetrabutyllead were produced. In similar experiments,not shown, poor current efficiencies were obtained with tetraphenyllead.Improvements in these runs are obtainable when the frequency of thealternating current is reduced to between 5 10 cycles.

EXAMPLE 2 In this series of experiments two cells of the type shown inFIG. 1 were arranged as shown in FIG. 3. To averaged the overallprocedure a partially direct current electrolyzed Grignard ethersolution was used as the feed in the first surge drum. The Grignardconcentration in the feed was 0.35 moles of methyl magnesium chloride.To this was added 1.5 percent of methyl chloride based on the weight ofthe Grignard. The first cell was operated for 2 hours under theconditions specified and the effluent therefrom which contained 0.1 1active Grignard and 0.4 percent methyl chloride was fed to the finalcell. This cell was operating in the effluent averated 0.02 moles ofmethyl magnesium chloride and 0.2 percent methyl chloride. The cellswhich are connected electrically in series were constantly monitoredwith respect to voltage drop and amperage. The following operationalparameters were established:

Average Range Temperature 133 F. l25-l40 F. Net Flow Rate 7.1 gm/min4.0-13.) grams/min Current 10 amps 9.5l().5 amps Voltage 52 volts 50-59volts Active Grignard* 0.02 0.0l0.04 moles/gm MeCl 0.15 nil-0.02

of final cell After this series of experiments was completed, the finalcell was dismantled and examined. The lead shot in the center bed wasclean and fluid, and no solids were indicated. However, the outer leadbed was cemented into a solid mass by magnesium salts and etherates.During the cell runs, it was noted that both temperature and voltageincreased. This apparently was due to solids coating the outer lead bedand reducing the circulation through the cell. No gas make was observedand the lead yield based on OH was high so the Wurtz losses wereinsignificant.

The following results were obtained from the runs:

Total Time 80.23 hours Total Weight of Effluent 34,262 grams Lead Yield(OH) 105 Current Efficicncy 77 (200 max) Magnesium Balance 101 TotalMass Balance 98 EXAMPLE 3 Using the experimental techniques shown inEXAM- PLE l, tetraethyltin and tetramethyltin were prepared.

CONCLUSIONS compounds. Thus if one were to electrolyze methyl magnesiumchloride and ethyl chloride using lead elec trodes a mixture ofmethyl-ethyl lead compounds would be produced.

By using the invention, it is possible to electrolyze with inexpensiveand available alternating current a solution of Grignard reagents andmetal electrodes to produce organometallic compounds. The efficiency ofthe reaction is surprising in that at the end of an electrolysis runlittle or no Grignard reagent remains.

We claim:

1. An electrolytic cell for producing organometallic compoundscomprising a substantially upstanding cylindrical metal vessel havingside, top and bottom walls, a perforate support within the vesselextending thereacross and spaced above the bottom wall, a plug ofinsulating material supported centrally of said perforate support, atubular perforate member of insulating material vertically extendingupwardly from the plug and defining with the plug a first chamber withinthe member and a second chamber with the perforate support and thevessel side walls, said tubular perforate member including a semi-rigidopen large mesh haircurler member, inner and outer layers of fine meshnylon screen along the inner and outer sides of said haircurler memberand supported thereby, the mesh of the screen layers being substantiallyfiner than the mesh of the haircurler member and such as to prevent themovement therethrough of the shot, a first lead electrode in the form ofshot within said first chamber, a second lead electrode in the form ofshot within said second chamber, means connecting said first and secondlead electrodes to a source of low frequency alternating currentpotential, an opening in the bottom wall, and an opening in the top wallfor permitting a Grignard reagent solution to flow through the vessel tobe electro lysed, whereby said perforate member provides a flow paththrough the cell for the solution.

2. The electrolytic cell as defined in claim 1, wherein said nylonscreens are about -80 mesh. and said haircurler member is ofpolypropylene.

3. The electrolytic cell as defined in claim 2, wherein said meansconnecting said electrodes to a source of alternating current potentialincludes a contact mounted on the vessel for said second electrode and acontact extending into said first electrode.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 853735 Dated December 10 1974 John C. Shepard, Jr., Inventor(s) Edward E.Johnson and Robert W. Bearman It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Col. 6, Table I, second to last line, delete "t8" before "0.29"; line54, change "averaged" to -simplify--; line 64, change "averated" to-averaged--; line 65, change "are" to -were--; Col. 7, line 5, change"4.0-l3.)" to --4.0l3.l--.

Signed and sealed this 15th day of April 1975.

(BELT- n-) Attest C. E-QIRfiiALL DANE RUTH C. Elfin-S 321 Commissionerof Patents rttestin; Ufficer and Trademarks F ORM PO-I 050 (10-69)USCOMM-DC 603764 59 U.S. GOVERNMENT PRINTING OFFICE II' O-Jll-Sll,

1. AN ELECTROLYTIC CELL FOR PRODUCING ORGANOMETALLIC COMPOUNDSCOMPRISING A SUBSTANTIALLY UPSTANDING CYCLINDRICAL METAL VESSEL HAVINGSIDE, TOP AND BOTTOM WALLS, A PERFORATE SUPPORT WITHIN THE VESSELEXTENDING THEREACROSS AND SPACED ABOVE THE BOTTOM WALL, A PLUG OFINSULATING MATERIAL SUPPORTED CENTRALLY OF SAID PERFORATE SUPPORT, ATUBULAR PERFORATE MEMBER OF INSULATING MATERIAL VERTICALLY EXTENDINGUPWARDLY FROM THE PLUG AND DEFINING WITH THE PLUG A FIRST CHAMBER WITHINTHE MEMBER AND A SECOND CHAMBER WITH THE PERFORATE SUPPORT AND THEVESSEL SIDE WALLS, SAID TUBULAR PERFORATE MEMBER INCLUDING A SEMI-RIGIDOPEN LARGE MESH HAIRCURLER MEMBER, INNER AND OUTER LAYERS OF FINE MESHNYLON SCREEN ALONG THE INNER AND OUTER SIDES OF SAID HAIRCURLER MEMBERAND SUPPORTED THEREBY, THE MESH OF THE SCREEN LAYERS BEING SUBSTANTIALLYFINER THAN THE MESH OF THE HAIRCURLER MEMBER AND SUCH AS TO PREVENT THEMOVEMENT THERETHROUGH OF THE SHOT, A FIRST LEAD ELECTRODE IN THE FORM OFSHOT WITHIN SAID FIRST CHAMBER, A SECOND LEAD ELECTRODE IN THE FORM OFSHOT WITHIN SAID SECOND CHAMBER, MEANS CONNECTING SAID FIRST AND SECONDLEAD ELECTRODES TO A SOURCE OF LOW FREQUENCY ALTERNATING CURRENTPOTENTIAL, AN OPENING IN THE BOTTOM WALL, AND AN OPENING IN THE TOP WALLFOR PERMITTING A GRIGNARD REAGENT SOLUTION TO FLOW THROUGH THE VESSEL TOBE ELECTROLYSED, WHEREBY SAID PERFORATE MEMBER PROVIDES A FLOW PATHTHROUGH THE CELL FOR THE SOLUTION.
 2. The electrolytic cell as definedin claim 1, wherein said nylon screens are about 60-80 mesh, and saidhaircurler member is of polypropylene.
 3. The electrolytic cell asdefined in claim 2, wherein said means connecting said electrodes to asource of alternating current potential includes a contact mounted onthe vessel for said second electrode and a contact extending into saidfirst electrode.